Millennium Line - Broadway Extension: Planning & Pre-Construction

[officedweller]

Originally Posted by SOSS

Why did they end up going with single vs twin for Evergreen? The single bore tunnel has nearly 3 1/2 times the material removal requirement then twin bore. Thoughts?

Like KPELLY said, timeline (the contractor agreed to an opening date and WILL pay penalties for the current delays) - it said to be an "innovation".

It's mentioned in the Partnerships BC report here:

7.3 Key Features of the Preferred Proponent’ Proposal
The preferred proponent submitted a strong technical submittal that clearly demonstrated the
consortium has the expertise and capacity to design and construct the Project. The technical submittal
included a single-bore bored tunnel (as opposed to the twin-bored tunnel contemplated in the
Province’s reference concept for the Project). This innovation brings schedule benefits to the Project,
significantly reduces the risk associated with achieving the required summer 2016 substantial
completion date, and creates an opportunity for early completion.

http://www.partnershipsbc.ca/projects/pr...on/evergreen-line-rapid-transit-project/

Ha!
Query whether the larger bore diameter caused the sinkholes and delays, or whether those would have occurred with a twin bore as well
(even further delaying the line if 2 passes were required and racking up even more penalties for the contractor).

So... getting back to the Broadway Line, if it's a P3 with contractors competing to open the line earlier as an advantage for their bid - we may just see a single bore instead of a twin bore to advance the timeline.

I would expect that if the Broadway Line is under 10th Ave., a single bore would take up a narrower RoW than a twin bore (except maybe at stations).

Also note that a single bore can accommodate stacked guideways and stations as was once suggested (but not implemented) for Toronto's Crosstown Line
(a SkyTrain stack would be narrower diameter due to lower ceiling heights - no caternary wires).
Note that the rendering would show an expanded tunnel section for a station - the regular bore would be narrower.


http://lrt.daxack.ca/blog/?p=109

[SOSS]

Interesting.... A stacked configuration could potentially allow for platforms on either side of the train to allow for quicker boarding at key locations (i.e. Broadway-City Hall Station).

[BCPhil]

You could just use 2 machines and get a twin bore done just as fast as a single tunnel. In fact I imagine that it would be faster as it would be removing less material in total. But, it would be higher upfront cost.

I think there are other technical benefits for the single tunnel on the Evergreen line, like they might have been worried about keeping the tunnels in parallel that far underground for so far, and building the escape corridors between tunnels (to escape fires) might be difficult that far bellow the surface (whereas you can just build doors in the divider wall you put in the tunnel). It is also a long way between stations there, and a single tunnel would allow them to put in a switch if they want.

But on the Broadway line I think the best option would be to use 2 machines. Removing that much dirt from right under the streets and buildings might cause larger problems than on the Evergreen line.

In Toronto, the crosstown line is using two machines, which made an odd surface appearance just a few days ago.

http://www.thestar.com/news/gta/2015/04/19/an-exciting-glimpse-at-boring-machines-on-eglinton.html

[officedweller]

Good point about cross-over tracks if the tracks are side-by-side in a single bore.

Simultaneous parallel bores would also require duplicate work crews (though for a shorter period).
I wouldn't necessarily look to Toronto for cost-effective rapid transit construction.

[VancouverOfTheFuture]

well the Canada-Line was a double bore and that seemed pretty successful. (the noncut-and-cover part)

[KPELLY]

I don't think the top speeds of smaller or larger diameter TBMs are that much different from what I've seen, however since you are displacing more volume, you would likely run into more issues and thus could affect the schedule. It is possible that using 2 TBMs could be faster, running them side by side would likely be the cheapest option of running 2 TBMs at the same time as you would only need one launch pit. (however I think overall, having to run 2 TBMs would be more expensive than 1).

One thing I'm wondering is if they could stagger the launches and have a Lead and a Lagging TBM so that they got a good idea as to what soil conditions they would encounter with the lagging TBM. Since they would know what was ahead, they could then prepare for it and make adjustments on the lagging TBM as necessary, that way only one TBM would have to go in blind (so to speak), and if the lead TBM encountered problems and got stuck for instance, hopefully they could make adjustments so that the trailing TBM wouldnt encounter those same problems or get stuck, and could even pass the lead TBM, making it now the lead TBM.

They would then hopefully avoid a situation where both TBMs became stuck at the same time from the same issue and avoid there being 2 crews sitting idol.

Because I know when they use one TBM, like for the Canada Line, they were able to make the second trip back a lot faster than the first trip because they knew what conditions to expect.

[officedweller]

Originally Posted by VancouverOfTheFuture

well the Canada-Line was a double bore and that seemed pretty successful. (the noncut-and-cover part)

An KPELLY mentioned, they used one TBM for Canada Line - and made 2 passes.

[VancouverOfTheFuture]

Originally Posted by officedweller

An KPELLY mentioned, they used one TBM for Canada Line - and made 2 passes.

couldn't they do the same thing for Broadway though? its really not that long of a stretch.

[officedweller]

Originally Posted by VancouverOfTheFuture

couldn't they do the same thing for Broadway though? its really not that long of a stretch.

For sure, if its 2 tubes, that's what they'll probably do - I thought you meant simultaneous.

[KPELLY]

The Millennium Extension to Arbutus would be about 5 kms of tunnel. The Canada Line was about 3 kms of bored tunnel. This has quite a large impact on whether or not they go with a single or dual bore.

Likely the reason they went with a single TBM and 2 passes on the Canada Line, is because its only 6 kms total of bored tunneling (2 passes), where as the entire line is 19 kms long, so even if they were only getting 40 metres per week average (including launch) they would still finish the tunnel (2 passes) in under 3 years and not affect the overall schedule. The Broadway Line is nearly entirely tunnel, so it therefore is critical path, so much more important that they finish it as quick as possible.

Once you are talking about 5 kms of skytrain (10 kms total bore), you would need to be getting average 60 - 70 metres per week average (including 2 launches) to finish the tunnel in 3 years, so if you run into issues and only achieve 40 metres per week, you end up with the tunnel taking close to 5 years to complete the 2 passes. Plus this adds the need to launch the TBM twice which brings down the average overall.

Where as if you go with a single bore large diameter tunnel on Broadway, you can finish the tunnel in 3 years with just 35 to 40 metres per week average, and the actual TBM rate can actually be much slower since you only need to launch it once.

They are somewhat lucky that they went with the single bore on the Evergreen Line, because they likely would have ran into most of these issues on the first pass, and would be even further behind as they would have had to do a whole other launch and pass. (granted they likely would have had less issues on the 2nd pass)

My bet would be them going with a single bore large diameter tunnel for Broadway, I think a stacked configuration would be cool, especially if they were able to have platforms on both sides of both tracks, but I think that is unlikely, it will probably end up being similar to the Evergreen Line Tunnel.

As an aside, came across this page that talks about Sydney's Rail line which has 15 kms of dual bored tunnel where they are planning to use 4 TBMs at the same time, so each would roughly travel 7.5 kms. Oddly enough, some are calling it "Skytrain" because ~4 kms is elevated.

http://www.tunneltalk.com/Australia-Skytrain-Apr12-Four-TBMs-for-Sydney-North-West-Rail-Link.php

[BCPhil]

Originally Posted by VancouverOfTheFuture

couldn't they do the same thing for Broadway though? its really not that long of a stretch.

It really depends on when you want to get it done.

The schedule of the Canada Line was still constrained by how long it took to dig the tunnels under downtown. It was one of the shortest sections of the line, but took the longest to complete. The rest of the line was pretty much done and ready while they finished up downtown. You could have run trains from Richmond to City Hall months before they were done downtown.

One of the drawbacks of doing 2 passes with 1 machine is you pretty much have to wait until the second pass passes the station pits before you can start construction. So you have to do one pass, then start the second before any work can start on the stations. Using 2 machines jumpstarts that process.

The other benefit of using 2 tunnels compared to one is that the 2 tunnels makes it easy to build center platforms instead of edge platforms. With a single platform you only need 1 elevator or escalator where you need 2 with side platforms. If the tunnel is not that deep, then it reduces the need for down and down then up access to the other platform (like at station on the Canada line: 41st, 49th). You add up all that construction cost across all the stations (plus future stations to UBC) and the savings could pay for a second machine, and get the project done faster (thus starting revenue generating faster as this line will make money from day one).

[twoNeurons]

10th Ave (the most likely route) is slightly above broadway. A cut n' cover station would allow for entrances on Broadway that would not require any stairs. I wonder if a stacked tunnel would allow for the same.

I don't think the stations will be tunnels anyhow. They'll likely be cut n' cover. As cut n' cover will allow stations to be shallower than the tunnel, allowing for the same energy savings that the Canada line takes advantage of when entering and leaving stations.

[Ridgerunner]

Everyone:

I have been monitoring the progress of the TBM on the Evergreen line.

In short ... no progress. They said in February ... a short wait for some cutter head maintenance. .. will re start in 4 weeks.

Then they said the same thing in April and May and also in June. There are cameras on the exit where the spoils are taken away. There has been no activity for 5 months now.

What seems to have happened is that some very soft soil has caused bubbles and pockets to appear which causes surface subsidence. This seems not to have been a problem in similar soil for the Canada line because the tunnels were only 6 meters wide.

But a ten meter wide tunnel has special problems for our kind of soil in the Lower Mainland. It does not work .. or at least .. it does not work very well.

The Evergreen project has been delayed from spring/summer 2016 to Fall of 2016 ... and counting.

This means that a single tunnel which is 10 meters wide is not a viable option for the Broadway route. The possibility of constant stoppages due to subsidence issues is a severe constraint.

Alice, the TBM on the Evergreen line, is a pain in the neck for Translink. The Evergreen bored tunnel is only 2 KM in length and is the obvious miscalculation on that line.

What happens when they try and address 5 KM to Arbutus or 12 KM to UBC.

They would be crazy to chance a 10 meter machine on that route.

This suggests that 10th avenue is back to being the viable alternative to Broadway. First of all, you can dig up 10th avenue all the way to UBC ... and ... who really cares.

If you don't go cut and cover, then a dual bore works as well.

My comments are just a hunch, of course. Any of you that have direct knowledge are welcome to post a reply to my comments.

Toodles.

[officedweller]

Actually, they have made progress.

End of January: under Cecile Drive
End of April: under Clark Dr. and Seaview Dr.
The next scheduled maintenance location is at Clarke Dr. and Robinson - in mid summer, so they are reinforcing that location too.

The issue is that whenever they stop for maintenance, they have to grout and reinforce the surrounding soil
- they didn't expect to have to do that so often.

But you are correct in that a single bore might pose similar issues IF the soil under 10th Ave/ Broadway is similar in nature.

Hopefully that will point them to cut and cover, which I think is feasible under 10th Ave.

[Zassk]

Originally Posted by officedweller

The issue is that whenever they stop for maintenance, they have to grout and reinforce the surrounding soil
- they didn't expect to have to do that so often.

It makes me wonder why they don't just "pre-grout" the whole rest of the route. Surely it should not be necessary to stop for months to prepare the soil like this. Surely it could be done preventatively before the TBM reaches a given spot in the dig.

[BCPhil]

One thing you have to ask though, is a long delay on a single tunnel still shorter than a short delay on 2 tunnels using 1 machine? If they were doing 2 tunnels on the Evergreen line, the TBM might not be delayed by as much (I doubt that a slightly smaller machine would have zero trouble in the same conditions), but it would have to go back to the start and go through that mess a second time.

Also, the tunnel ranges in depth from 17m to 60m under the surface. At Cecil Drive it was 40m below the surface, and at Seaview it is 50m down (that is about 15 stories below ground). That is a long way to drill to do some simple shoring up around the machine.

The Canada line only went 30m max under ground. The Broadway extension would be even more simple. It would be much easier to perform rescue work and other work above the machine as it would only be a several stories underground and directly below the street most of the time.

[officedweller]

Good point - or versus the cost of 2 TBMs

Originally Posted by Zassk

It makes me wonder why they don't just "pre-grout" the whole rest of the route. Surely it should not be necessary to stop for months to prepare the soil like this. Surely it could be done preventatively before the TBM reaches a given spot in the dig.

They did pregrout at Seaview - but they still had issues.
They are pregrouting at Robinson - probably more than they did at Seaview.

[Ridgerunner]

Everyone

Doers anyone know why the screwup with having to grout the way for Evergreen happened?

I downloaded a study with all kinds of pretty drawings explaining the various layers of soil, gravel, sand and clay that they would find.

Missed the issue, didn't they.

With a cut and cover along 10th avenue (starting at Main Street), grouting , of course, is not an issue. And neither is disruption of commercial operations.

perhaps cheaper too.

Maybe the money they save on cut and cover, they can drive the system all the way to UBC.

[officedweller]

Because the tunnel is twice the diameter as, say, the Canada Line tunnel.

When they do maintenance, the soil/rock above the TBM (or in front of the TBM?) needs to be self-supporting (because it's at the front of the TBM, so no concrete tunnel segments hold the soil in place).

The workers create a void space to be able to access the cutter heads at the front of the TBM (not sure if they reverse the TBM to create the gap or access the cutting face from behind).

The larger diameter unsupported tunnel seems to be unable to support itself - so they need to reinforce it. (i.e the grouting has nothing to do with tunnel segments (it's not like grouting tiles) - it's injecting concrete to stabilize the soil around the TBM so when the void is created, the cavern can support itself.)

Think of tunneling a cave (or snow cave) without ceiling supports - but increasing the clear span - will it still support itself? That's the difference between what was expected and what happened.

[city-dweller]

Originally Posted by Ridgerunner

Maybe the money they save on cut and cover, they can drive the system all the way to UBC.

Well pour some fuel on the bore vs. cut and cover debate why don't you?

But seriously, I don't like the idea of the Arbutus - UBC section being part of a future phase. They need it sooner to address the UBC density and the upcoming Jericho development. I would love the three local First Nations to badger the Feds about this. They could be a great ally in getting the line all the way to UBC. The university has been lobbying the province and Translink about a direct line more vocally recently. I grew up in the Jericho area and every UBC consultation/open house about transportation devolves into when are we going to get better rapid transit.

The opponents have typically been those worried about the associated density the line would bring west of Arbutus. The density issue is really a building form issue. Building 3-4 minimum storeys in the Jericho Lands and higher in the UBC/Musqueam lands would easily support the Alma and UEL stations and address these concerns. There is also the underdeveloped W10th Safeway property with surface parking all around the store. Prime development for around the Sasamat station. The Macdonald Station is the only one that does not lend itself well to towers, but it is the main transfer point for the #2/#22. And, I do see it guiding infill in the area. Look at some of the Expo line stations.